Hey sgan
You'll need to log a support case via MYOB Practice to transfer ownership of a file to the client, this will allow the client to pay for the subscription themselves. More information can be found on this page.
In order to remove a file showing on your practice list, your user access to the file will need to be removed. We can help you out with this as well, just raise a support case from your MYOB Practice dashboard and we'll be in touch to sort things out.
Reach out if you have any more questions!
Cheers, Amanda.